Games are freezing my computer :(

Nature of freezing: Screen freeze and continuous sound loop, ctrl+alt+delete doesnt work, mouse doesnt work, can only get out by resetting computer.

I just got a new system that I've put together.

i7 920
Asus p6t deluxe
Zotac GTX 295
WD 1T
750W PSU
Antec Skeleton
Vista home premium 64bit

The computer will run fine normally. If I play a game for around 1 hour it will freeze and enter sound loop. This same freeze and sound loop will also happen sometimes if I try to install 1+ items at once. Or say if I were to unzip a large file while installing another file it will sometimes freeze. This morning I was unzipping a file and watching a movie and it froze.

Drivers are up to date (that I know of), I've done a few scans to check. Bios is the latest version.
Memory diagnostic test and hd error check came up with nothing. I tried to do a stress test with everest a few times but computer crashes.

All I'm doing at the moment is typing this message, and the current temp readings are (Celsius):
Motherboard: 42
CPU: 35
CPU (individual cores): 37-38
GPU1 and 2= 53 and 51
HDD: 37

Note: I'm in Queensland, Australia, and this room is about 30 Celsius. From what I've read, my temps are pretty normal and lower than one other people achieve.


Any ideas on what I can do to fix this?

i have my motherboard sitting on a metal sheet instead of being screwed in so it isnt touching. The instructions say to screw it in so it isnt touching. surely that would have no effect?

well it's an antec skeleton so the motherboard is placed laying flat. There's a gtx295 card connected to the motherboard which is quite heavy. The screws supplied are also very small. All this together makes it impossible to screw it in so it isnt touching the metal plate, because the motherboard bends from the weight of the graphics card.

Can the bottom of the motherboard touching a metal plate cause problems? Does anyone else have it set up like this without freezing issues?

This may sound stupid to you but I had the same problem pretty much same specs accept my GPU is a Palit GTX 295 and I have 1000w PSU.
Took me ages to figure it out but it turned out it was the Automatic Time Sync for the clock in the bottom right. to fix it i just unchecked the synchronize time with internet time sever box. You should try this IMO what can you loose?